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CGA Emulator for the HP 95LX Possible?

CGA Emulator for the HP 95LX Possible?

Why not create a CGA emulator for the HP 95LX. That way, more DOS software would be able to run on the original Palmtop.

Ariel L. Dembling

Buenos Aries

[Your idea of a CGA emulator, for the HP 95LX, is an idea that Mark Scardina, Dave Goodman, I, and a number of other programmers explored almost two years ago. Unfortunately none of us were able to get this idea to work.

The HP 95LX's screen is hard-wired to be a monochrome display. Trying to make it behave as a CGA monitor is no small task. If all programs that ran on a CGA color monitor used the ROM BIOS to write to the screen, there might be a way to get them to work on the HP 95LX. However, most CGA programs write directly to the screen memory (IBM refers to these programs as "ill-behaved".) Running such programs on the HP 95LX would cause the computer to lock up.

Even if it were possible to find a work-around for ill-behaved programs, the results would not be satisfactory. Screen updates would be too slow. The performance of the HP 100LX confirms this assertion. The 100LX operates as a graphics monitor. It is slow even though the computer is running at twice the speed of the HP 95LX, and is using a built-in, graphics co-processor (a bit blitter is the name given to such a co-processor.)

There have been several graphics libraries for HP 95LX programmers. These libraries have been mentioned in the Palmtop Paper (see pg. 49, M/J 93, PRGTOOL1&2.ZIP (ON DISK ICON).) They all use the built in ROM BIOS routines to write to the screen. The routines are well-behaved, and relatively fast.

Lotus 1-2-3 does a good job of creating graphics on the 95LX. It uses the ROM-BIOS routines built into the 95LX.

In short, the way to create graphics on the 95LX is to use the methods detailed in the HP documentation for System Developers. To run ill-behaved, CGA programs on a palmtop computer, you'll need an HP 100LX -- Ed Keefe.]

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